Using two large glass measuring cups or pitchers, fill one 1/4 of the way with hot tap water and the other with cold tap water. Hold a thermometer in the pitcher with hot water and pour the cold water into the hot water until the thermometer reads 80 degrees F. Using a kitchen scale, weigh out the required water in a large bowl. Add the instant yeast to the water and give it a quick swirl with your finger.
(Note: I am assuming a room temperature of 70 degrees F here. If your room temperature is higher you will need slightly cooler water, if you room temperature is lower you will need slightly warmer water.)
Weigh the spelt, einkorn and rye flour in a medium bowl and whisk or mix with your hands to combine. Add the flours on top of the water and yeast. Finally, add the salt on top of the flour. Mix the dough together with your hands until evenly combined. Cover with a kitchen towel and let the dough rest for 30 minutes so the flour can absorb the water.
Lightly flour your work surface and scrape the dough out on to it. Gently knead the dough for a couple of minutes until it has tightened up and feels smooth. Place the dough back in the bowl and cover with plastic wrap, beeswax wrap, a large dinner plate or something else that will keep the moisture from escaping and the top of the dough from drying out.
Let the dough rise on the counter for 12 hours or until it has doubled in size and the surface is dotted with bubbles.
Lightly flour your work surface again and scrape the dough on to it. Using a metal dough scraper or large knife, divide the dough into two equal pieces. Fold the dough over onto itself and turn it over. Round the dough by sliding the dough scraper or your hands underneath the far side of it and gently pulling it towards you. Give it a quarter turn and repeat this process all around the dough until you have a nice tightened round. If the dough is not catching as you pull, scrape away some of the flour on your work surface and try again. Repeat with the other piece of dough. Dust each with flour and cover with a kitchen towel. Let rest for 30 minutes.
Lightly flour your work surface. Working with one dough at a time, turn it over so the smooth side is facing down. Fold the dough like a letter, bringing one side of the dough into the middle and then the other side on top. Turn and fold the dough this way in the other direction then turn it over so the seams are facing down. Round the dough by sliding a dough scraper or your hands underneath the far side of it and gently pulling it towards you. Give it a quarter turn and repeat this process all around the dough until you have a nice tightened round. If the dough is not catching as you pull, scrape away some of the flour on your work surface and try again. Repeat with the other piece of dough. Place each dough round into a floured proofing basket (or a bowl lined with a floured kitchen towel) seam side up. Cover both lightly with plastic wrap or a plastic produce bag cut open (if you have it). Let rise for one hour.
While the dough is rising, place two dutch ovens, including the lids, into the oven and pre-heat to 500 degrees F (or as high as your oven will go). Position the rack in the lower third of the oven. (Note: if you only have one dutch oven you will bake the loaves back to back instead of at the same time). To test if the dough is ready, press, do not poke, the tip of one wet finger quickly and lightly, about half an inch, slightly off center, into the crown of the dough (area of maximum expansion). If the indentation remains but springs back just slightly, the dough is ready to bake. If the dent fills in, give the dough another 5-10 minutes to rise and re-test.
Remove the plastic covering from your dough. Generously flour your work surface and tip both doughs (or just one if you are baking them back to back) onto it with the seam sides down. Remove the hot dutch ovens and place the lids beside them. With a lame or razor blade score the doughs with two deep slashes in the shape of a X (or another pattern). Pick them up one at a time and very carefully lower them into the dutch ovens. Replace the lids, slide them into the oven, lower the temperature to 475 degrees F and bake for 25 minutes.
After 25 minutes remove the lids and continue baking for another 15 to 20 minutes until the loaves are a deep chestnut colour. Remove from the oven and use pot holders to carefully lift the breads out and place them on a rack to cool thoroughly. If you have an instant read thermometer, the breads are done when the internal temperature is 190-200 degrees F.